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Discussion Starter · #1 ·
I just purchased a 99 Legacy Outback 2.5 with 185k. It had a few maintenance items to fix, but it ran fine. I have driven it a whole 65 miles and when I took off from a stop light today I starting hearing this really loud banging/popping sound. I pulled into a parking lot and couldn't find anything. I limped it home about a mile away and noticed that it only happened while moving and was loud if I was accelerating and would change that way it sounded, but was still loud when decelerating. If I was coasting and giving it just a little bit of gas it would quiet down. Right close to the house it started to get really loud and shake the car violently. When I got home I noticed that the passenger side CV axle boot was ripped apart and there is some play in the axle. Will this be my only problem or should I look elsewhere while also fixing this?
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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front diff

driveshaft

the other axle



Um, is this an automatic?

are all 4 tires the same brand with the same amount of wear?

do you 'feel' any jerkiness when this sound happens?

can you get someone to pace the car, listen to the noise and try to pinpoint if it's left side, right side, front , cente or rear?


post your city and someone may be able to suggest a shop that can take a look.
 

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Discussion Starter · #4 ·
It is an automatic. All 4 tires are the same and worn evenly. There is no left/right jerkiness. Noise sounds front and center.

I took a video from inside the car, I was moving very slow:

 

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In the video, the car is barely moving -- just going into the garage from the looks of it. The rate of the knocking seems too high to be a wheel or axle. Sounds much more like the propeller shaft.

Some quick math. There's 10 - 12 knocks over what appears to be the length of the garage, say 18 - 20 feet. The circumference of the tires is probably in the 80 - 84 inch range, or about 6+ feet. So the wheels/axles would rotate 3 - 4 revolutions. But the propeller shaft turns about 4 times the rate of the wheels, which would be 12 - 16 revs in the same distance. That's more like the rate of the knock.

Check for worn/broken u-joint (there's two or three) on the drive shaft, or something in contact with the drive shaft that shouldn't be (heat shield?). Otherwise, it could be a damaged rear differential (pinion shaft/gear), or a problem in the transmission.
 

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A CV joint has multiple edges on the joint if one is bad you could get a pop for every edge on the joint/socket ie multiple pops for one turn of the wheel. Just thinking the simple most obvious item the CV joint is still a prime suspect and would be the first major item I would check before getting crazy on more costly stuff.
 

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Discussion Starter · #9 ·
I got all 4 wheels off the ground and was able to take a video of it in motion. I put a reference mark on the tire to show it spinning while hearing the noise. I am sure it is not the rear drive shaft as it was not moving when I was taking the video. To me it sounds like the noise was coming from in the transmission, but I would like an idea of what it is before I dive in.
 

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front diff

bet you can make a little noise/feel a pop turning the front wheel by hand.
 

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The wheel marks didn't come out too well when trying to compare to the rate of the knocking sound. But the fact that the rear drive wasn't moving certainly eliminates it.

I noticed, in the video, that while the left wheel was turning, the right (seen only partially) wasn't, or at least didn't appear to be.

The suggestion to turn the wheel by hand is right on the mark.

Try first with the transmission in Park (automatic) or in gear (manual) and engine off. (With a manual, also set the parking brake to prevent the rear drive from turning.) The other wheel should turn in the opposite direction. This will check the differential side gear and spider gears, as well as, possibly, the axles.

If there's no noise, set the transmission in neutral, block or lower the other front wheel so it can't turn, and see if the raised wheel can be turned. If the noise appears as the wheel is turned, then it suggests there's a problem in the crown gear and/or pinion gear or pinion shaft. At this point, while monitoring the number of times the wheel is turned, count the knocks. Continue until there's a good number of wheel revolutions and clicks. The ratio can help narrow down exactly where the clicking is coming from. (Much the same as I referred to earler about the rear drive.)
 

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Discussion Starter · #12 ·
In the video the passenger wheel was barely moving.

Ok, so here is what I just tried:

1) Turned the drivers side wheel both forward and back, the other wheel turned opposite. No noise and smooth.
2) Stopped the passenger wheel from turning and turned the drivers wheel forward and back. No noise and smooth.
3) Turned the passenger wheel F/B without the driver wheel being blocked, the driver wheel did not turn. No noise and smooth.
4) Went back to the driver wheel turned it F/B and the passenger wheel did not move. No noise and smooth.
5) I tried all of the this in neutral, reverse, and drive with the engine off as well and the results were the same as 3 & 4.

Also don't know if this is normal, but it made this noise while in reverse and drive:

 

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The buzzing is probably one of the transmission solenoids. It will do this if the key is at ON, and the transmission is set to R or D. The tests I suggest do not require the key to be at ON; only at ACC to allow the gear lever to be moved between N and P.

With the engine off, neutral, reverse and drive are all the same. What is needed are tests in Park.

Tests in Park:

Front wheels raised, free to turn, gear in Park. Rotate one wheel; the other should turn the exact same number of revolutions in the opposite direction.

Then block one wheel from turning, and try to turn the free wheel -- it should not turn.

Repeat on both sides.

Note: when rotating a wheel by hand, don't rock it forward and back -- turn it steadily in one direction at least four or five revolutions. (It can be turned in the opposite direction as well, but again, for a number of revolutions, not just back and forth .)
 

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If you examine the drain plug for the front diff, you might see pieces on it instead of just a thimble -full of sludge.

kinda weird there's no noise turning by hand- but to me, it looked a LOT like an 'approx.' 4:1 ratio'
 

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I just purchased a 99 Legacy Outback 2.5 with 185k. It had a few maintenance items to fix, but it ran fine.
what were these maintenance items? Did anyone drain/refill the transmission or other fluids? has the front diff fluid level been checked?
 

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Discussion Starter · #16 ·
The buzzing is probably one of the transmission solenoids. It will do this if the key is at ON, and the transmission is set to R or D. The tests I suggest do not require the key to be at ON; only at ACC to allow the gear lever to be moved between N and P.

With the engine off, neutral, reverse and drive are all the same. What is needed are tests in Park.

Tests in Park:

Front wheels raised, free to turn, gear in Park. Rotate one wheel; the other should turn the exact same number of revolutions in the opposite direction.

Then block one wheel from turning, and try to turn the free wheel -- it should not turn.

Repeat on both sides.

Note: when rotating a wheel by hand, don't rock it forward and back -- turn it steadily in one direction at least four or five revolutions. (It can be turned in the opposite direction as well, but again, for a number of revolutions, not just back and forth .)
I started all of the tests in park, then when the opposite wheel stopped moving I tried the rest to see if I could get it moving again including returning to park. No luck.
 

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Discussion Starter · #17 ·
what were these maintenance items? Did anyone drain/refill the transmission or other fluids? has the front diff fluid level been checked?
They were:
-Oil and filter change
-Oil and filter change (tranny)
-New pads/rotors all around
-Replace power steering pump
-New battery and terminals

I have not checked the front diff level. I will do next time I'm out.
 

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They were:
-Oil and filter change
-Oil and filter change (tranny)
-New pads/rotors all around
-Replace power steering pump
-New battery and terminals

I have not checked the front diff level. I will do next time I'm out. The transmission had me worried a bit because when I went to the parts store they said it took 2 quarts of mercon vi with a filter change. After it broke and I was reading I noticed it takes 4 quarts of mercon iii. I filled it up but of course no change.
the stick for the diff is on the other side (pass side for US) and can sometimes be hard to find if it's covered in grime.
 

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I started all of the tests in park, then when the opposite wheel stopped moving I tried the rest to see if I could get it moving again including returning to park. No luck.
Do I understand correctly:

The transmission was in Park with both front wheels raised. One front wheel was rotated, and the other front wheel turned in the opposite direction then stopped. After that, the other wheel would not turn again when the first wheel was turned (it could still be turned with the gear still in Park).

If this is correct, then there's a possibility that a CV joint in the axle to the is broken but I think it's more the internal gears of the differential could be damaged.
 

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Discussion Starter · #20 ·
Do I understand correctly:

The transmission was in Park with both front wheels raised. One front wheel was rotated, and the other front wheel turned in the opposite direction then stopped. After that, the other wheel would not turn again when the first wheel was turned (it could still be turned with the gear still in Park).

If this is correct, then there's a possibility that a CV joint in the axle to the is broken but I think it's more the internal gears of the differential could be damaged.
The opposite wheel stopped turning by hand in any gear/park after test #2.
 
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